In the world today there are between 17 and 20 million slaves. That is, people who have no civil rights, are indentured in that they owe money, and don't have the ability to change their jobs at will until their debts are paid off. And, more shocking for people in Britain, they're all around us.

But people can't quite believe it. They don't see the migrant labourers being bussed off to work in farms or care homes, so they don't think they really exist. And even if they know they do, it's another stretch to imagine just how awful their conditions really are.

Before I started research for Ghosts, I found myself thinking that maybe it's easier for the Chinese or Romanians to leave their children behind – maybe family doesn't mean to them what it does to us. But when you meet them, they're beside themselves with grief, missing the families that they've left behind to try and support.

I worked with them undercover for a while, pretending to be South African, first up in Liverpool with people still working as cockle pickers, and then down near Birmingham with people picking spring onions. I was pretty hopeless at it. The Chinese, on the other hand, were fantastic: very clean and hard working. I was exhausted. We were getting up at 5.30am, at work by 7am. There were probably six or seven hundred of us picking away, with two toilets and no drinking water. You'd finish about 7pm. And then most people would go and work in a book factory, eventually getting some rest – if they could, in such overcrowded accommodation – at about 4am.

But modern slavery isn't just bad for those who are being exploited. It's bad for the people doing the exploiting. And the people who are blindly part of the system. I think on the whole British people are a very fair and kind, but there's a lack of understanding about how widespread this problem is. I thought the reports were all exaggerated. I thought it was left-wing extremists stirring up trouble. It isn't.

And that's dangerous. When people don't feel a part of another culture, aren't educated into our way of thinking and have no investment in the country, it's very easy for them to be antagonistic towards it. Ghettoising people is never a good idea. And these people feel a huge resentment against the west, against the greed that it represents. The kinder we are, the less likely we are to have aggressive behaviour coming back in our direction; terrorism, even. The more humane we are to people the nicer they are back to us. This is a problem that will come to haunt us unless we do something about it soon.

Maybe the changes we're experiencing at the moment will help this. Perhaps the new economic regulation will translate into labour regulation. If we pride ourselves on living in a civilised country we need a realistic minimum wage, maximum working hours and proper healthy and safety regulations, and these must apply to migrant labour. There needs to be an understanding that our economy would collapse overnight if we didn't have these people doing the shit jobs that no one else does. There needs to be recognition of mutual dependency. Legislation needs to reflect that. Most importantly, our attitudes need to change. And fast.